If the antenna is like most it probably doesn't have a set screw to hold it at the right length for a give SWR (that's of course not taking into account when the antenna is tightened all the way to the base). As per channel 19, it may be very busy when you try and access it, or it could be the antenna itself. Going with a better antenna (preferably one that uses a different mount type) will probably help alot. If you've got an SWR meter just stick with the Maxon until you can test it out with a better antenna.